The agriculture industry has devoted considerable resources toward the development of phenotypically distinct plants with economically advantageous qualities. Valuable features in food crops include increased vigor, disease resistance, greater yields, extended shelf-life, and enhanced nutritional content.
The development of high yielding food crops is particularly important. Each year, the tillable land available for agricultural production is reduced as more acreage is devoted to alternative uses. At the same time, the human population is rapidly increasing. Therefore, it is essential to increase agricultural productivity in order to meet the nutritional needs of the world's burgeoning population.
Efforts to develop crop plants that produce higher yields have been directed toward pest control, or toward the selection and breeding of varieties that bear greater numbers of fruit, or that produce larger fruit. These crop breeding endeavors are very time-consuming and labor-intensive, but have historically increased crop yields incrementally over time. Modern techniques of recombinant DNA manipulation and genetic engineering offer the prospect of the more rapid creation of new plant varieties with novel traits.
Photosynthesis in plants is a critically important biosynthetic process upon which virtually all living organisms depend for our very existence. Photosynthesis occurs in the chloroplasts of plant cells. In the process of photosynthesis, energy in the form of light is converted to ATP, which fuels a series of enzymatic reactions that catalyze the synthesis of carbohydrates. Molecular oxygen (O.sub.2) is an essential byproduct of photosynthesis. Since photosynthesis is the source of metabolic energy in plants, photosynthetic efficiency is a significant factor associated with general plant growth and vigor.
It is known that photosynthetic activity is positively correlated with chloroplast number (Leech and Baker, "The development of photosynthetic capacity in leaves. In: J. E. Dale and F. L. Milthorpe (eds), The Growth and Functioning of Leaves. Cambridge University Press, Cambridge. pp 271-307, 1983). Despite the centrality of the photosynthetic function of chloroplasts to life, relatively little is known about the manner in which chloroplast number and size are regulated.
Chloroplasts are also the site of several important biochemical processes in plant cells that contribute to nutritional content of CRO plant. Amino acids and lipids are synthesized in chloroplasts. Plastids are also the site of synthesis of some important secondary metabolites and vitamins.
What is needed in the art is a means for manipulating the number and size of chloroplasts in agronomically and horticulturally important plants to achieve greater plant productivity and nutritional quality.